fn main() {            //<1>
    let a = 10;          //<2>
    let b: i32 = 20;     //<3>
    let c = 30i32;       //<4>
    let d = 30_i32;      //<5>
    let e = add(add(a, b), add(c, d));
  
    println!("( a + b ) + ( c + d ) = {}", e);
  }
  
  fn add(i: i32, j: i32) -> i32 {    //<6>
    i + j                            //<7>
  }